Technical Field
Embodiments of the invention relate generally to imaging and more specifically reducing radiation scatter in an x-ray imaging system.
Discussion of Art
During medical diagnostic radiography processes, x-rays are directed toward an object from an x-ray source. When x-rays are used to create an image of an object, a portion of the radiation passes directly through the object from the x-ray source and onto an x-ray detector or film to create an image. Some of the direct radiation is differentially absorbed by the object, which creates an image of the object on the detector or film. A portion of the radiation, however, is scattered and arrives at the x-ray detector at an angle that deviates significantly from its original path from the x-ray source. As will be appreciated, this scattered radiation reduces contrast of the radiograph image and can potentially affect image quality.
Many medical x-ray imaging systems use a post-patient collimation device to reduce the scattered radiation reaching the detector. Such imaging systems often use a removable x-ray grid, i.e., an “anti-scatter grid,” as the collimation device. Anti-scatter grids are typically fabricated from thin strips of x-ray absorbing material, e.g., lead, that are arranged in a geometric pattern to absorb scattered radiation. These grids also include a non-absorbent spacer material between the x-ray absorbing strips that allows direct radiation to pass through the grid.
The strips in an anti-scatter grid, however, are all directed or angled to a fixed distance. That is, the grids have a fixed focal distance, i.e., a focal length, from the x-ray source. Ideally, the x-ray source is positioned from the grid/detector assembly at this focal length to achieve optimal radiograph results. In many x-rays systems, however, the x-ray source to detector distance, (“SID”), is variable and can be greater or less than the fixed focal length of the grid. For example, in interventional x-ray imaging systems, the SID varies typically from 85 cm to 125 cm. Given this range, in many such systems, a general-purpose anti-scatter grid is utilized at a fixed focal length typically of 100 cm. The further away the grid/detector assembly is from the grid focal length, however, the more the grid attenuates primary radiation at the periphery of the field of view.
In certain types of imaging modes, such as Cone Beam CT mode “CBCT”) imaging, the use of specific grids that are focused at a particular SID that may be different from general purpose grids would be highly desirable. Moreover, in certain circumstances, such as pediatric or extremity imaging, it may be desirable to image a subject without a grid. As will be appreciated, obtaining optimal image quality and/or radiation dose in view of these considerations may necessitate replacing or substituting the anti-scatter grid during operation.
What is needed, therefore, is an apparatus and method that facilitates the use of multiple anti-scatter grids during operation of an imaging system.